In the past, liquid crystals constituted by calamitic molecules comprising a plurality of benzene or cyclohexane molecules with modifying groups at both ends have been used in liquid crystal displays and like, for example. Adjustments to viewing angle and contrast of the display are made by causing the calamitic liquid crystals to orient in a uniform direction.
In the past, to orient the liquid crystal molecules, an alignment film comprising, for example, a polyimide or the like, is formed on the surface of the glass substrates for sandwiching the liquid crystals, thereby orienting the liquid crystal molecules in a predetermined direction coincident with the alignment direction of the alignment film, through sandwiching of the liquid crystals between the alignment films.
In one example of a production method adopted when forming an oriented film on the surface of a glass substrate, a polyimide solution, for example, is coated and baked onto the glass substrate, forming a polyimide film (alignment material film) several tens of nanometers thick, and thereafter the surface of the polyimide film (alignment material film) is rubbed in one direction with a rubbing roller having cloth wound about the surface (for example, Patent Document 1).
However, with methods that involve orienting the liquid crystal molecules by forming an alignment film on a glass substrate surface, due to the adoption of production methods like that described above to form the alignment film, the alignment film may become scratched by rubbing cloth that is shed by the roller as it is rubbed or by dust sloughed off from the polyimide film or the like, or the dust itself may become deposited on the surface of the alignment film. A resultant problem is that this tends to lead to display nonuniformities and display defects of the liquid crystal display.
In order to solve this problem, there has recently been proposed a technique, called photoalignment, which uses ultraviolet light to align the alignment material film. Specifically, by irradiating an alignment material film of polyimide, azobenzene, or the like with linear polarized or unpolarized ultraviolet light, the alignment material film becomes aligned in the same direction, due to its photodegradation characteristics. Consequently, alignment films of good alignment can be formed by a non-contact process, preventing display nonuniformities and display defects of the liquid crystal displays and the like.
However, with photoalignment, in the event that the alignment material film is irradiated with ultraviolet light exclusively from a single direction, the alignment direction of the alignment film will be a single direction only, and therefore the liquid crystal molecules sandwiched between the alignment films will orient in a single given direction exclusively. A consequent problem is that the liquid crystal display or the like will have a narrow viewing angle.
In order to solve this problem, there has recently been proposed an alignment material film exposure technique called multidomain alignment (for example, in Patent Documents 2 to 4). FIG. 9 is a schematic view showing exposure in conventional multidomain alignment, wherein FIG. 9(a) is a side view showing multidomain alignment exposure in a conventional exposure unit, and FIG. 9(b) is a perspective view thereof. As shown in FIG. 9, in an exposure unit of employing a multidomain alignment system, exposure light 11a, 12a from two different light sources (a first light source 11 and a second light source 12) is output at mutually different output angles, whereupon the exposure light 11a, 12a is transmitted through a mask 13 disposed between the first light source 11, the second light source 12, and a member for exposure 2. FIG. 10 is a drawing showing the mask in this multidomain alignment system exposure unit, and an alignment film formed by a single exposure. As shown in FIG. 9(b), the mask 13 is constituted by a frame 130 and a pattern formation portion 131 at the center thereof; as shown in FIG. 10, a first light-transmitting region group 131a and a second light-transmitting group 131b in each of which a plurality of light transmission regions are arrayed in one row are formed in the pattern formation portion 131, in correspondence with the respective exposure light from the first light source 11 and the second light source 12. The first light-transmitting region group 131a and the second light-transmitting group 131b are disposed spaced apart in the relative scanning direction of the alignment material film with respect to the mask 13, with the respective plurality of light transmission regions corresponding to regions split to one-half the picture element width. The light transmission regions of the first light-transmitting region group 131a and the second light-transmitting group 131b are arrayed with gaps between them, so that there is no overlap in the scanning direction. As shown in FIG. 10(b), the respective light transmission regions of the first and the second light-transmitting group 131a, 131b are formed such that a plurality thereof (in FIG. 10(b), six) are lined up in the scanning direction. By irradiating these respectively different regions 131a, 131b of the mask 13 from different directions with the exposure light 11a, 12a from the first and second light sources 11, 12, the light transmitted through the light transmission regions irradiates and exposes the alignment material film on the surface of the member for exposure 2, which is supported on a stage 15. In so doing, through a single exposure, in both the direction of split (width direction) of the picture elements and the lengthwise direction perpendicular thereto (the scanning direction), respectively, the alignment material film is exposed by the exposure light transmitted through the plurality of light transmission regions, forming an alignment film in such a way that a plurality of regions, which correspond to picture elements and have uniform alignment direction, line up in the width direction and lengthwise direction, as shown in FIG. 10(c).
In this case, due to the respectively different angles of slope of the exposure light 11a, 12a with respect to the surface being exposed, an alignment film aligned in two directions is obtained. Consequently, sections that will constitute the R (red), G (green), and blue (B) picture elements of a liquid crystal display or the like are split into halves respectively irradiated by the exposure light 11a, 12a. In so doing, two alignment directions of the alignment film are created within each single picture element of the liquid crystal display or the like, and the liquid crystal molecules can be oriented in two directions. In so doing, the viewing angle of the liquid crystal display or the like can be made wider. Moreover, in a multidomain alignment system exposure unit such as this, rather than lining up a plurality of the light transmission regions of the mask shown in FIG. 10 in the scanning direction, the light transmission regions could instead be constituted to extend in the scanning direction, making these light transmission regions correspond to regions that include a plurality of pixels lined up in the scanning direction; and by continuously transmitting light through these light transmission regions, regions having uniform alignment directions can be formed in the alignment film so as to extend in a band in the scanning direction. In so doing, an alignment film in which each of the regions that will constitute adjacent pixels in the width direction has a different alignment direction is manufactured.